Treatment of cellulose esters



materially increased.

Patented May 14, 1935 UNI E STATES TREATMENT or csLLULoss reruns Camille Dreyfus, New York, N. Y., and Leslie N. Lee, Cumberland, Md.,' assignors to; Celanese Corporation of America, a corporation of Delaware v 7 No Drawing.

Application February 26, 1929, sci-mm. 342,932 r Y Claims. (c1. 260--102) This invention relates to. the treatment of organic esters of cellulose, and relates more particularly to subjecting such cellulose esters to a treatment whereby their resistance to heat is Anobject offour-invention is to treat organic esters of: cellulose bytreating with certainacid ties that tend to solutions whereby at least-some of the impuriimpair. their resistance to heat is removed. T

In theiorniation of organic esters of cellulose, cellulose is treated with an'esterifying agent in the presence of a catalystthat promotes esterification. The catalysts mostcommonly usedare sulfur compoundsand particularly sulfuric acid. After the esterificationjsome of the sulfur'compounds used a as catalysts enter into reaction with the cellulcse'to form sulpho compounds of cellu 1ose,- and these' sulpho-compounds greatly diminish the resistanceofgtheicellulose esters to the action V-ofheat. Wehave found that if the esters ofcellulose arejtreated with suitable concentra tions of solutions of certain acids at suitabletem-;

peratures, a large percentage of. the sulfur compounds are removed, and .the heat'test or the esters of cellulose have been prepared in the presence ofa. sulfur containing catalyst such as sulfuric acid. These, esters of cellulose may be treated at any stage of their treatment after their formation; that is, they may be treated prior to ripening to desired solubility, if such treatment is carried out, or they may be treated at any time subsequent thereto.

The oxygen containing acids that we prefer to employ are oxalic acid, phosphoric acid, nitric acid or any suitable'mixture of theseacids, al though other acids may also be employed. These acids may also be employed in admixture with a quantity of sulfuric-acid. As to the concentration of the acids employed, in the aqueous treating bath, they may be varied within wide limits, ranging from 0.5 to or more, depending on the natureof the acid and the temperatureemployed.

.b'y bur invention, whi h-c e acetate is such .as benzol. After the mechanical removal at which-thev cellulose, acetate first chars cras- -.Thus in the case of phosphoric acid or acid,

if the solution of the same islappliedat temperatures, 3 to 8% concentration will be found suitable. I

The ester of cellulose to be treated in accord- 5 v ance with our invention'ma'yj be made in any ir n e and s-previously stated may be treated by ourprocessin any stag e'of: t great p mentgf'Thus a cellulose acetateimay-be formed by the treatment of a suitable cellulosic material .with acetic anhydride; anda catalyst in the presence of a solvent such as glacial acetic 7 acid so that theicellulose acetate-thatfi's formed becomes dissolved in the acetylating mi ;ture. l6-

After completionof the acetylation, the cellulose acetate may be ripened by the addition of asuitable amountof water or any other suitable agent until it reaches thestage of solubility in organic solvents thatis desired, whereupon the cellulose acetate may be precipitated by the addition of a .large amount of water vanother precipitating agent. This cellulose acetatemay then-be treated by our process, or it may be flrst washed-and "ground and then treatedby our process. a

; If desired, theorganicesterof cellulose maybe formed by esterifying the same in the presenco of diluents that are not. solvents for thefester of cellulose so'that the organicester of cellulose does not-dissolve in'the acetylating mixture. Thus '3 cellulosea'cetate maybe formed by treating cot.-

ton or other cellulosic material with acetic anhydride and a catalyst in the presence of a diluent of the cellulose acetate from theacety'latinz ture. the same may be treated byour process either before or after washing. with: water;

As aniexample ofthe advantages of 2 our proof, ess, it is pointed outthat a cellulose acetate hav ing a heat test for 180C; and aso, content of 0.45% before being treated byeourbstabilizing process has a heat test' of 215 C. to 250 C. or more and a SOr content of 0.l0 to 0.02% less. v The term heat test indicates the temperatures sumes a dark' colora' a In; order further to illustrate our invention but without being limited thereto, the following specific examplesaregiven. a

v "Example I 1 v a A cellulose acetate prepared by-treatment of. cotton with acetic anhydride and sulfuric acid as catalyst in the presence of a diluent maybe treated by our invention. This cellulose acetate 66 c I I may be formed by the treatment of 50 parts of cotton linters with an acetylating mixture comprising 190 parts of acetic anhydride, 210 parts of acetic acid, 750 parts of benzol and 2.5 parts of sulfuric acid. These parts are by weight. The acetylation is carried out at temperatures from 11 C. to 50? C. for about 24 hours. The cellulose acetate thus formed is separated from the acetylating liquors by extraction in a centrifugal basket and is then washed free from the acid and benzol.

The cellulose acetate thus formed has a heat test of 189 to 192 C. and a S04 "content of 0.44%.

The cellulose acetate thus produced is boiled for V .1 Example III ITI1Q cellulosei acetate described in, Example I is boiled for 7 hours in an aqueous solution containing 5% of phosphoric'acid and 1% of "nitric acid'ior 7 hours; The cellulos e acetate now has a heat'test of 238 to 241 C. and a 80;. value of 0.02%." T

I Having described our invention, what we claim and desire to secure by Letters Patent is: V

Method of preparing an organic ester of cellulose of high resistance to heat comprising esterifying cellulose in an esterifying bath containing sumcient non-solvent for the cellulose ester to be formed so that the same does not enter into solution, ,mechanically separating" the cellulose ester formei'and treating the same while insolid form with a solution of an oxygen-containing acid having'a dissociationconstant greater than 1.0 x. .1l 0 ,at a ternperature substantially that of the boilingpoint of the solution; a

2. Method' of preparing cellulose acetate of high resistance to heat comprising acetylating cellulose in an ace'etylation bath cdntaihing'sufii- 'cient non-solvent for the cellulose acetate tobe formed so that the same do'esnot enter into solution, mechanically separating the cellulose acetate, and treating the "same while in solid form with a solution of an "oxygen-containing" acid having a dissociation constant greater than 1.0 x 10- at a' temperature substantially that of the boiling point of the solution. 1 3'; Method of preparing cellulose acetate of high resistance to heat 'comprisingacetylating cellulose'in an acetylation'bath containing sufucient non-solvent for'the cellulose acetate to be-formed so that the same does not enter into solution, mechanically separating the cellulose acetate and treating the same while in solidfor rn with a solution' of nitric acid at a temperature substam tially that of the boiling point of the solution.

4. Method 'of preparing cellulose acetate of high resistance to heat comprising acetylating cellulose in the presence of a sulfur-containing catalyst in an acetylation bath containing sufficient non-solvent for'the cellulose acetate to be formed so that the same does not enter into solution, mechanically separating the cellulose acepointof the solution.

tion of phosphoric acid at a temperature substantially that of the boiling point of the solution.

6. ,Method of preparing cellulose acetate of high resistance to heat comprising acetylating cellulose in thepresence of a sulfur-containing catalyst in an acetylation bath containing sufficient non-solvent for the cellulose acetate to be formed so that the same does not enter into solution, mechanically separating the cellulose acetate and treating the same while in solid form with anaqueous phosphoric acid of 3 to 8% concentration at a temperature substantially that of the boilingpoint of the solution.

[Method of preparing cellulose acetate of high resistance to .heat comprisingv acetylating cellulose in an acetylation bath containing suf- -ficient non.-solvent forthe cellulose acetate to be formed so that'the samedoesnot enter into solution, mechanically separating the cellulose acetate and treating the same while solid form with a solution of oxalic acid at a temperature substantially. thatof the boiling point of the solution.

8. Method of preparing cellulose acetate of high resistance to heat comprising acetylating cellulose in the presenceoi. a sulfur-containing catalyst in an acetylation'bath containing sufficient nonesolvent for thecellulose acetate to be formedso that thesame does not enter into solution, mechanically separating the cellulose acetate and treating the same while. in solid form with aqueous oxalic acid of 3 to 8% concentration at a temizwrature substantially that of the boiling 9..Method of preparing an organic ester of cellulose of high. resistance .to heat; which comprises 'esterifying cellulose in an' esterifying bath containing sufiicient non-solvent for the cellulose ester to be formed so that the same does not enter into solution, mechanically separating the cellulose ester formed, and treating the same while in solid form with a solution of an oxygen-containing acid, having a dissociation constant greater than 1.0 x 10 of 0.5-20% concentration at a temperature substantially that of the boiling point of the's'olution. V 7

- 10. Method of preparingan organic ester of cellulose of high resistanceto heat, which comprises'esterifying cellulose in an esterifying bath containing suificientnon-solvent for the cellulose ester to be formed so that the same does not enter into solution, mechanically separating the cellulose ester formed, and treating the same while in solid iorm with a solution of an oxygen-containing acid, having a. dissociation constant greater than 1.0 x 1O of 3-8 concentration at a temperaturesubstantially that of the boiling point of the solution. I v

CAMILLE DREYFUS.

LESLIE N. 

